This invention relates generally to fuses and, more particularly, to fuses with a fuse state indicator.
Fuses are widely used as overcurrent protection devices to prevent costly damage to electrical circuits. Fuse terminals typically form an electrical connection between an electrical power source and an electrical component or a combination of components arranged in an electrical circuit. A fusible link is connected between the fuse terminals, so that when electrical current flowing through the fuse exceeds a predetermined limit, the fusible link melts and opens the circuit through the fuse to prevent electrical component damage.
A large number of fuses for a given electrical system are typically contained within a fuse box, and an accompanying chart lists the particular electrical devices corresponding to the fuses contained in the box. After one or more of the fuses has opened a circuit, the chart must be reviewed to discover which particular electrical device or devices in the system are not working, and the chart must then be matched against the fuse box to locate the responsible fuse or fuses. Aside from a fuse box chart, traditional fuses do not offer an adequate indicator to determine the state of a fuse, i.e., whether a given fuse is operable or inoperable. For fuse boxes that do not contain such a chart, in order to determine if a fuse is operable, or which fuse is inoperable due to an opened fuse link, each individual fuse must be removed from the fuse box and tested or replaced, which is a monotonous, time consuming process that sometimes must be repeated before locating an inoperable fuse or fuses.
While some fuse indicators have been developed for use with cylindrical cartridge fuses, recent fuses have been developed which are rectangular in shape, such as a fuse described in commonly owned U.S. Pat. No. 5,841,337. Because the rectangular fuses are relatively new to the art, a fuse indicator is needed to accommodate these fuses.
Accordingly, it would be desirable to provide a less complicated and more reliable fuse indicator system that can accommodate both a cylindrical cartridge fuse and a rectangular fuse.
In an exemplary embodiment of the invention, a fuse state indicator includes a fuse casing having a substantially transparent lens. A combustible substance is disposed adjacent the lens and substantially coextensive therewith. A secondary fuse circuit is electrically connected in parallel with a main fuse circuit, and includes a fuse wire which is disposed adjacent the combustible substance. A noncombustible material of a contrasting color relative to the combustible substance is disposed adjacent the combustible substance and substantially coextensive therewith so that an opening of the main fuse circuit causes the fuse wire of the secondary fuse circuit to melt, thereby igniting the combustible substance. After combustion of the combustible substance, the non-combustible material is revealed through the transparent lens to indicate that the fuse is inoperable and has opened a corresponding circuit.